Alas, porting Zeta-C to Common Lisp is not nearly as easy as one might expect. The problem is that a lot of C code makes assumptions about how the compiler is laying stuff out in memory -- for example, code might write a word through an int pointer, then read it back as bytes through a byte pointer. To support this kind of thing, Zeta-C used displaced arrays with different element types onto the same memory locations, which the Symbolics hardware supported but which can't be done in Common Lisp. (It didn't even quite work on the CADR and Lambda, as they were 32-bit machines; it requires that the tag bits be in addition to the low-order 32 bits of a word, as they were on the 36- and 40- bit Symbolics hardware, rather than borrowed from them.)

I suppose, though, that if there's only one chunk of C code you care about compiling this way, there is a chance you could get lucky, in that the code might not do anything that wouldn't work in CL.